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# Windup hard disk

Prolongs battery life.
 (+8) [vote for, against]

The computer hard disk has platters inside that have to be spun up to speed before data transfer can take place. This requires energy, supplied by the battery. And battery capacity is a constraint.

Now, if you could provide a spring to store energy, clockwork to make those disks spin and a handle to wind up it will take a lot of the load off that battery.

The winding handle could be designed as a lever, projecting from the right hand side of the screen. As you are typing the story of your life into it it senses that the hard disk spring needs another wind and moves the cursor to the extreme right of the screen. The winding motion is a push on the lever towards the left. You will have to do this periodically, every time the cursor reaches the right edge.

 — neelandan, May 28 2002

Data plunger http://www.halfbake...idea/Data_20plunger
The windup hard disk's lever reminded me of this. [beauxeault, May 28 2002, last modified Oct 04 2004]

 When my CD walkman is running low on batteries I usually start it up with a little manual spin to conserve energy, although it can be counter productive if you spin it the wrong way.

I like the idea of having a lever on the side of your computer - it's kind of reminiscent of typewriters where you slide the barrel back every line. You could also do it with a flywheel and pedal a la pottery wheel.
 — stupop, May 28 2002

 Hrm. Considering that a laptop hard drive draws an average of 3W or so during operation (more during spin-up), we need to provide about 3 J/s. If we assume a 35 cm distance for the lever to travel, and that the lever provides 30 N of resistance (the equivalent of lifting a ~3 kg laptop straight up by the same distance)...scribble, scribble...we'd need to push the lever every 3 seconds.

 I guess it would give me the exercise I've been looking for, but I think I'll stick with the untried-but-true, half-baked laptop crank generator.

Caveat: it's been ten years since I've taken a physics class. Results may vary.
 — francois, May 28 2002

Every 3 seconds? My goodness, that would be a hard disk.
 — bristolz, May 28 2002

Problem: The hard drive platters need to spin at an absolutely constant speed. Massive data corruption and nasty such stuff can occur if they don't.
 — Corona688, Dec 07 2002

I can hear the nerds wheezing from here.
 — TBK, Dec 08 2002

 // Problem: The hard drive platters need to spin at an absolutely constant speed. Massive data corruption and nasty such stuff can occur if they don't. //

 Hard drives usually use three-phase brushless motors. Even with the fanciest drivers (which most hard drives don't use) you do get some measurable torque ripple, and therefore speed ripple.

In a hard drive, one entire side of a platter is dedicated to a servo pattern. The head on that side is usually only equipped for reading, not for writing, so you can figure out which side it is if you disassemble a drive. Anyway, this is to enable the hard drive to figure out where its heads and platters are in relation to each other at any moment, and control them to where it wants them to be to read/write at a given location on the other platter sides. In this way, I imagine it can (and does) overcome some speed ripple.
 — notexactly, Jan 23 2019

Best done in an hydrogen/helium enclosure, of course.
 — FlyingToaster, Jan 23 2019

Followup to my previous statements—something I just realized now when rereading what I wrote: Speed ripple is probably completely repeatable, because the platters are rigidly affixed to the motor, and the motor is driven at a nominally constant speed during operation. Therefore, if the hard drive just ignores the speed ripple, this is probably fine, because the effect of it will always be the same. It will just result in slightly different recording densities at different azimuths on the platters. It is probably even naturally accounted for in the servo pattern writing process, because (IIRC) the hard drive uses its own motor to rotate the platters at its nominal speed, and the external machine only controls the arm. (That's why there's a kidney bean-shaped hole in the top cover with a silver sticker over it. That's where the machine reaches in to grab the arm.)
 — notexactly, Jan 24 2019

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